<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>三角</title>

    <style>
        .box1 {
            width: 0;
            height: 0;
            /* border: 10px solid pink; */
            border-top: 10px solid pink;
            border-right: 10px solid red;
            border-bottom: 10px solid green;
            border-left: 10px solid blue;
        }

        .box2 {
            margin-top: 100px;
            width: 0;
            height: 0;
            border: 50px solid transparent;
            border-top-color: pink;
        }

        .box3 {
            margin-top: 30px;
            width: 0;
            height: 0;
            border: 50px solid transparent;
            border-left-color: red;
        }

        .box:hover .sanjiao {
            display: block;
        }

        .box:hover .bottom {
            display: block;
        }

        .box {
            background-color: pink;
            /* display: none; */
            margin: 30px auto;
            position: relative;
            width: 150px;
            height: 220px;
        }

        .sanjiao {
            display: none;
            position: absolute;
            top: -10px;
            left: 50%;
            margin-left: -10px;
            width: 0;
            height: 0;
            border: 10px solid transparent;
            border-bottom-color: red;
        }

        .bottom {
            display: none;
            position: absolute;
            top: 10px;
            width: 150px;
            height: 200px;
            background: red;
        }
    </style>

</head>
<body>
    
    <div class="box1"></div>
    <div class="box2"></div>
    <div class="box3"></div>

    <a href="#">显示下拉</a>
    <div class="box">
        <div class="sanjiao"></div>
        <div class="bottom"></div>
    </div>

</body>
</html>